The present invention relates to methods of making signs using retroreflective cube corner sheeting, and in particular using such sheeting that uses a specularly reflective layer on the cube corner faces.
The term xe2x80x9csignxe2x80x9d as used herein refers to a stand-alone article that conveys information, usually by means of alphanumeric characters, symbols, graphics, or other indicia, and that in use is mounted to an object such as a post, bracket, wall, or similar body. Specific examples include signs used for traffic control purposes (STOP, YIELD, speed limit, informational, roadside markers, etc.), street signs, and vehicle license plates. The term xe2x80x9cretroreflectivexe2x80x9d as used herein refers to the attribute of reflecting an obliquely incident light ray in a direction antiparallel to its incident direction, or nearly so, such that it returns to the light source or the immediate vicinity thereof.
Two known types of retroreflective sheeting are microsphere-based sheeting and cube corner sheeting. Microsphere-based sheeting, sometimes called xe2x80x9cbeadedxe2x80x9d sheeting, employs a multitude of microspheres typically at least partially imbedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes, vapor coats) to retroreflect incident light. Illustrative examples are disclosed in U.S. Pat. No. 3,190,178 (McKenzie), U.S. Pat. No. 4,025,159 (McGrath), and U.S. Pat. No. 5,066,098 (Kult). In contrast, cube corner retroreflective sheeting comprises a body portion that has a structured surface comprising a plurality of cube corner elements. Each cube corner element comprises three approximately mutually perpendicular optical faces that cooperate to retroreflect incident light. Usually, but not always, the body portion has a substantially planar front surface and a back surface that coincides with the structured surface. Examples include U.S. Pat. No. 1,591,572 (Stimson), U.S. Pat. No. 4,588,258 (Hoopman), U.S. Pat. No. 4,775,219 (Appledorn et al.), U.S. Pat. No. 5,138,488 (Szczech), U.S. Pat. No. 5,213,872 (Pricone et al.), U.S. Pat. No. 5,691,846 (Benson, Jr. et al.), and U.S. Pat. No. 5,696,627 (Benson et al.).
Cube corner sheeting can be further categorized by the mechanism by which each face of a given cube corner element reflects light. In one category, reflection is provided by total internal reflection (xe2x80x9cTIRxe2x80x9d). In this case the cube corner element is a pyramidal structure composed of a transparent material, and the reflective face at issue is the boundary between the transparent material and a benign air (or other low refractive index medium) environment. Co-pending U.S. application Ser. No. 09/087,683 discusses this category of cube corner sheeting.
The present application is directed to the other category of cube corner sheeting, in which reflection is provided by a thin layer of specularly reflective material disposed on the cube corner element faces. Aluminum, silver, gold, copper, and the like, or a combination thereof, and even non-metals such as a multilayer dielectric stack, can be vapor deposited or otherwise applied to the cube corner element faces and used as the specularly reflective material. Regardless of the type of specularly reflective material used, such sheeting is referred to herein as metalized cube corner sheeting, even if the specularly reflective material does not comprise a metal.
Currently, in the manufacture of retroreflective signs using metalized cube corner sheeting, a sign board is provided which comprises a rigid mass of metal, wood, plastic, or the like. xe2x80x9cSign boardxe2x80x9d as used herein means a rigid substrate suitable for mounting in the intended end use application. Metalized cube corner sheeting is then provided, such sheeting having itself been manufactured in separate steps to include: at least a first polymeric layer having a smooth front surface and a rear structured surface defining pyramidal cube corner elements; a thin layer of aluminum applied to the structured surface; a layer of pressure sensitive adhesive (xe2x80x9cPSAxe2x80x9d) applied to the aluminum layer; and a release liner at the back of the sheeting that covers the PSA layer. Such metalized sheeting is then prepared by removing the release liner so as to expose the PSA layer. The sheeting is applied to a smooth, flat front surface of the sign board with the adhesive layer contacting such front surface. Letters, symbols, or other indicia may be added in layers above the first polymeric layer either before or after the sheeting is applied to the sign board.
There is a continuing need to reduce the cost of retroreflective signs and to simplify the manufacture thereof.
Methods are disclosed herein in which the separate steps of applying an adhesive and a release liner to the metalized cube corner sheeting can be eliminated. Instead, a retroreflective sign is manufactured by: coextruding a rigid substrate layer and an adhesive layer, the rigid substrate layer being suitable for use as a sign board; providing a cube corner sheeting having a structured surface including a plurality of cube corner elements, the cube corner elements having a specularly reflective material thereon; and applying the retroreflective sheeting to the adhesive layer. The rigid substrate preferably comprises a polyolefin material, and in one embodiment is extruded to include channels therein for improved rigidity at reduced weight and cost. The adhesive layer exhibits high bonding strength to the cube corner sheeting and to the rigid substrate layer, and can comprise one or more individual layers. The adhesive layer can comprise a heat activated, pressure sensitive, or other suitable adhesive.
The method is useable with metalized cube corner sheeting in which the structured surface is formed in a back surface of the sheeting, wherein the cube corner element faces form pyramidal projections in such back surface. The method is also useable with metalized cube corner sheeting in which the structured surface is formed in a front surface of the sheeting, wherein the cube corner element faces form a cavity in such front surface.